WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.19 - Chromium oxides and hydroxides. - Chromium trioxide 2819.90 - Other 28 19.10 (A) CHROMIUM OXIDES z (1) Chfomium trioxide (chromium (VI)oxide) or chromic anh dride (Cr03) (wrongly known as chromic acid ", because it can give the cbromates of eading 28.41). Orange or red slabs or needles; deliquescent; very soluble in water; specific avity about 2.8. When combined with alcohol it gives explosive mixtures. An oxi ising agent in organic chemistry (manufacture of isatin, indi o dyes, etc.); also used in medicine and, when mixed with kieselguhr (" epurite "1, for puri$ing acetylene. 8J (2) Dichromium trioxide, chromium (III) oxide (chromium ses uioxide) (Cr203).Obtained by calcining chromates with an ammonium salt or by reducing ichromates. A very hard, olive green product, in owder or in crystals; insoluble in water; specific gravity about 5. The pure oxide is useif as a pigment known as " chromium oxide green ", not to be confused with mixtures of lead chromate and iron blues known as chrome green ". It is also used for the preparation of paints and printing inks, and in the porcelain, glass (coloured optical glass) or rubber industries. Because of its hardness and its resistance to heat, it serves for the reparation of abrasive compounds and refractory bricks for metal furnaces. It is also use for obtaining anti-rust products, and in chromium metallurgy. " f Chromite, natural chromium oxide containing iron (chrome iron ore, iron chromite) is excluded (heading 26.10). (B) CHROMIUM HYDROXIDES The term " chromium hydroxide " applies to the various hydrates of the oxides described above and, in particular, the green hydrate of chromic oxide (Cr203.2H20),obtained by treating potassium dichromate with boric acid; this is used as colouring matter under the name of" chrome green " or in the manufacture of Guignet's green. There is also a violet chromium hydroxide.
1.- Except where the context otherwise requires, the headings of this Chapter apply only to : (a) Separate chemical elements and separate chemically defined compounds, whether or not containing impurities; (b) The products mentioned in (a) above dissolved in water; (c) The products mentioned in (a) above dissolved in other solvents provided that the solution constitutes a normal and necessary method of putting up these products adopted solely for reasons of safety or for transport and that the solvent does not render the product particularly suitable for specific use rather than for general use; (d) The products mentioned in (a), (b) or (c) above with an added stabiliser (including an anti-caking agent) necessary for their preservation or transport; (e) The products mentioned in (a), (b), (c) or (d) above with an added anti-dusting agent or a colouring substance added to facilitate their identification or for safety reasons, provided that the additions do not render the product particularly suitable for specific use rather than for general use.